Use high-quality balancing machines, balancing to high standards and motor operating speeds

   Noise and vibration arise when the shaft center does not coexist with the axis of rotation. Balance has limited impact on efficiency, but affects operating noise and life expectancy, which is also important for maximizing the use of resources. Bearing vibration readings are usually taken in three planes: vertical, horizontal and axial. Vertical vibration may indicate a mounting problem, horizontal vibration may indicate a balance problem, and axial vibration may indicate a bearing problem. Balance at operating speeds is important because centripetal forces in the bearings can also cause imbalance.

Optimum Design of Rotor Lamination Exhibiting Sinusoidal Magnetic Field

Synchronous motors with high-performance permanent magnets have sinusoidal flux distribution and electromotive force. For distributed windings, the stator windings are usually the same as the asynchronous motor windings, which reduces vibration, noise and maintenance costs and improves overall performance.

Selection of Rare Earth vs. Ferrite (Ceramic) Magnets

Neodymium, rare earth, samarium cobalt magnets, or ferrite (ceramic) magnets are used in motors. Rare earth magnets are two to three times stronger than ferrite or ceramic permanent magnets, but are more expensive. Samarium cobalt magnets are the best choice for high temperature applications because of their high energy density, temperature resistance from 250 to 550, small decrease in parameters due to temperature increase, and oxidation protection, choosing samarium cobalt or neodymium as motor magnets is Depending on operating temperature, corrosion resistance and required performance. Low grade neodymium magnets may start to lose their "strength" if heated above 80, high grade neodymium magnets work at temperatures below 220. Ferrite or ceramic magnets are widely accepted due to their strong electrical resistance, good demagnetization, high corrosion resistance and low cost. Magnetic loss occurs when operating at temperatures above 250, but returns when the magnet is cooled to a lower temperature. Unless the circuit is designed for extreme conditions, the low temperature of -40 may cause a permanent loss of permanent magnet strength.

The motor needs an inverter

The inverter drive unit is lossless in no-load operation/standstill, and energy savings of up to 30% are expected by replacing existing line-fed three-phase drives. The characteristics of the drive unit make it ideal for driving pumps and fans in continuous operation. No additional components such as encoders are required. A footprint of up to 25% allows for a more compact machine design. The motors are well controlled and combined with a sensor less drive controller unit, they offer excellent real-world performance even at low speeds, with impressive dynamics under pulsed loads and speed changes.

Choose an inverter that can provide sensor less operation

 The drive can "self-detect" and track the permanent magnet position of the rotor. This is essential for smooth starting of the motor, while also allowing optimum torque to be produced and thus optimum efficiency. The absence of position or speed sensors reduces cost and increases drive system reliability. As efficiency continues to increase, it becomes increasingly important to program the controller settings for a specific motor for optimum efficiency.

Discrimination and Analysis of the Disadvantages of Permanent Magnet Motors

Permanent magnet motors (PMMs) generate torque through the interaction of stator current with permanent magnets on or within the rotor. It is common for small, low-power motors to be used for surface rotor magnets in IT equipment, business machines, and automotive auxiliary equipment. Internal magnets (IPMs) are common in large machines such as electric vehicles and industrial motors.

In PM motors, the stator may use concentrated (short pitch) windings if torque ripple is not a concern, but distributed windings are common in larger PM motors.

Since permanent magnet motors do not have a mechanical commutator, the inverter is essential to control the winding current. Unlike other types of brushless motors, permanent magnet motors do not require current to support their magnetic field.

So, if small or light, permanent magnet motors provide the most torque and are probably the best choice. No magnetizing current also means higher efficiency at load at the "sweet spot" - i.e. where the motor performs best.

Furthermore, while permanent magnets bring a performance advantage at low speeds, they are also a technical Achilles' heel. For example, as the speed of a permanent magnet motor increases, the back EMF approaches the inverter supply voltage, making it impossible to control the winding current. This defines the base speed of a general permanent magnet motor, and in surface magnet designs typically represents the maximum possible speed for a given supply voltage.

At speeds greater than base speed, the IPM uses active field weakening, in which the stator current is manipulated to deliberately depress the magnetic flux. The range of speeds that can be reliably implemented is limited to around 4:1. As before, this limit can be achieved by reducing the number of windings turns and accepting greater cost and power loss in the inverter.

The need for field weakening is speed dependent and has associated losses regardless of torque. This reduces efficiency at high speeds, especially at light loads.

In electric vehicles driving on the highway, this is very serious. Permanent magnet motors are often favored for EVs, but the efficiency benefits are questionable when real drive cycles are calculated. Interestingly, at least one prominent EV manufacturer has switched from PM to induction motors.

 Other disadvantages include the fact that it is difficult to manage under faulty conditions due to its inherent back EMF. Even if the frequency converter is disconnected, as long as the motor is spinning, current will continue to flow through the faulty winding, causing cogging torque and overheating, both dangerous.

For example, field weakening at high speeds can lead to uncontrolled power generation due to drive shutdown, and the DC bus voltage of the inverter can rise to dangerous levels.

Except for those permanent magnet motors that incorporate samarium cobalt magnets, operating temperature is another important limitation. And high motor currents due to inverter failure can cause demagnetization.

Maximum speed is limited by mechanical magnet retention. If a permanent magnet motor is damaged, repairing it often requires a return to the factory because safely extracting and handling the rotor is difficult. Finally, recycling at end-of-life is cumbersome, although the current high value of rare earth materials may make such materials more economically viable.

Despite these drawbacks, permanent magnet motors remain unrivaled in low speed and sweet spot efficiency, and they are useful in situations where size and weight are critical.




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